ex-04: Check for negative numbers

exercise-04-multiplication-table/main.c

@@ -2,10 +2,10 @@
 #include <stdio.h>
 
 int main() {
-	int range;
+	int range = -1;
 
 	printf("Rozsah:\n");
-	if (scanf("%d", &range) != 1) {
+	if (scanf("%d", &range) != 1 || range <= 0) {
 		printf("Nespravny vstup.\n");
 		return EXIT_FAILURE;
 	}